I. Chimeric and Transgenic Animals
Recent advances in recombinant DNA and genetic technologies have made it possible to introduce and express a desired gene sequence in a recipient animal. Through the use of such methods, animals have been engineered to contain gene sequences that are not normally or naturally present in an unaltered animal. The techniques have also been used to produce animals which exhibit altered expression of naturally present gene sequences.
The animals produced through the use of these methods are known as either "chimeric" or "transgenic" animals. In a "chimeric" animal, only some of the animal's cells contain and express the introduced gene sequence, whereas other cells have been unaltered. The capacity of a chimeric animal to transmit the introduced gene sequence to its progeny depends upon whether the introduced gene sequences are present in the germ cells of the animal. Thus, only certain chimeric animals can pass along the desired gene sequence to their progeny.
In contrast, all of the cells of a "transgenic" animal contain the introduced gene sequence. Consequently, every transgenic animal is capable of transmitting the introduced gene sequence to its progeny.